Diffusion barrier collar for interconnects

ABSTRACT

Representative implementations of techniques and devices are used to reduce or prevent conductive material diffusion into insulating or dielectric material of bonded substrates. Misaligned conductive structures can come into direct contact with a dielectric portion of the substrates due to overlap, especially while employing direct bonding techniques. A barrier interface that can inhibit the diffusion is disposed generally between the conductive material and the dielectric at the overlap.

PRIORITY CLAIM AND CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. § 119(e)(1) of U.S. Provisional Application No. 62/569,232, filed Oct. 6, 2017, which is hereby incorporated by reference in its entirety.

FIELD

The following description relates to processing of integrated circuits (“ICs”). More particularly, the following description relates to techniques for processing dies or wafers in preparation for bonding.

BACKGROUND

Dies or wafers, and the like, may be stacked in a three-dimensional arrangement as part of various microelectronic packaging schemes. This can include stacking one or more dies or wafers on a larger base die or wafer, stacking multiple dies or wafers in a vertical arrangement, and various combinations of these. Dies may be stacked on wafers or wafers may be stacked on other wafers prior to singulation. The dies or wafers may be bonded in a stacked arrangement using various bonding techniques, including using direct dielectric bonding, non-adhesive techniques, such as a ZiBond® direct bonding technique or a DBI® hybrid bonding technique, both available from Invensas Bonding Technologies, Inc. (formerly Ziptronix, Inc.), a subsidiary of Xperi Corp. (see for example, U.S. Pat. Nos. 6,864,585 and 7,485,968, which are incorporated herein in their entirety).

When bonding stacked dies or wafers using a direct bonding technique, it is desirable that the surfaces of the dies or wafers to be bonded be extremely flat and smooth. For instance, the surfaces should have a very low variance in surface topology, such that the surfaces can be closely mated to form a lasting bond. It is also desirable that the surfaces be clean and free from impurities, particles, and/or other residue. The presence of undesirable particles for instance, can cause the bond to be defective or unreliable at the location of the particles. For instance, some particles and residues remaining on bonding surfaces can result in voids at the bonding interfaces between the stacked dies.

Respective mating surfaces of the bonded dies or wafers often include embedded conductive interconnect structures, or the like. In some examples, the bonding surfaces are arranged and aligned so that the conductive interconnect structures from the respective surfaces are joined during the bonding. The joined interconnect structures form continuous conductive interconnects (for signals, power, etc.) between the stacked dies or wafers. However, due to the use of fine pitch conductive interconnect structures, the placement accuracy limitations of pick-and-place tools, contact grid patterns on the die or wafer surfaces, dissimilar pad sizes, and the like, a conductive interconnect pad of one die or wafer may be offset, or partially overlay the dielectric portion (e.g., silicon oxide, etc.) of the mating surface of the other die or wafer, rather than perfectly aligning with the respective conductive interconnect pad on the mating surface of the other die or wafer.

Misalignment such as this can cause the conductive material (e.g., copper, or the like) of the overlaying interconnect pad to diffuse into the dielectric that it comes into contact with, potentially resulting in degraded performance of the microelectronic structure. For example, the barrier properties of silicon oxide can degrade significantly (versus silicon nitride, silicon oxinitride, silicon carbonitride, etc.) at higher temperatures (such as during annealing) and within an electric field, promoting the diffusion of the conductive material into the silicon oxide. This can result in leakage, shorting between interconnects, and the like. The performance degradation can be particularly problematic when it involves multiple conductive interconnect structures of bonded stacks of dies or wafers, which can adversely affect package yield and package performance.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is set forth with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The use of the same reference numbers in different figures indicates similar or identical items.

For this discussion, the devices and systems illustrated in the figures are shown as having a multiplicity of components. Various implementations of devices and/or systems, as described herein, may include fewer components and remain within the scope of the disclosure. Alternately, other implementations of devices and/or systems may include additional components, or various combinations of the described components, and remain within the scope of the disclosure.

FIG. 1 is a profile view of a pair of stacked substrates showing a misalignment of embedded conductive structures within the stacked substrates.

FIG. 2 is a graphical flow diagram illustrating an example process of forming a microelectronic assembly comprising a pair of substrates with embedded conductive structures.

FIGS. 3A and 3B are profile views showing example barrier interfaces employed with stacked substrates having embedded conductive structures, according to various embodiments.

FIGS. 4A-4E are profile views showing example barrier interfaces employed with stacked substrates having embedded conductive structures, according to additional embodiments.

FIG. 4F is a plan view showing an example barrier interface with multiple embedded conductive structures, according to an embodiment.

FIGS. 5A-5C are profile views showing example barrier interfaces employed with stacked substrates having embedded conductive structures, according to additional embodiments.

FIG. 6 is a graphical flow diagram illustrating an example process of forming a microelectronic assembly comprising a pair of substrates with embedded conductive structures with a barrier interface, according to an embodiment.

FIG. 7 is a graphical flow diagram illustrating an example process of forming a microelectronic assembly comprising a pair of substrates with embedded conductive structures with a barrier interface, according to another embodiment.

FIG. 8 is a flow diagram illustrating example processes for forming a microelectronic assembly comprising a pair of substrates with embedded conductive structures and a barrier interface, according to various embodiments.

SUMMARY

Various embodiments of devices and techniques reduce or prevent conductive material diffusion into insulating material or dielectric of bonded substrates. Particularly, the devices and techniques disclosed herein mitigate undesirable diffusion due to misaligned conductive structures on the bonding surfaces of the substrates. The misaligned conductive structures can otherwise come into direct contact with a dielectric portion of the surfaces of the substrates due to overlap, especially while employing direct bonding techniques.

The devices and techniques comprise the use of a barrier interface disposed generally between the conductive material and the dielectric that can inhibit the diffusion of the conductive layer into surrounding dielectric materials.

The substrates may be dies, wafers, carriers, large flat panels, or the like, comprised of a semiconductor or a non-semiconductor material. Semiconductor materials may, for example, comprise direct band gap or indirect band gap semiconductors and their combinations thereof. Non-semiconductor materials may comprise, for example, a dielectric material for example, glass, ceramic, silicon oxycarbides, silicon oxide, or the like, or combinations thereof. The use of the term “substrate” herein is intended to include all of these and other like examples.

In an embodiment, a microelectronic assembly can include at least a first substrate having a first substantially planar surface, the first substrate comprising an insulating material or dielectric, for example. The dielectric may be provided on a base die or wafer of semiconductor, insulating, or conductive material. A second substrate has a first substantially planar surface, the second substrate also comprising an insulating material or dielectric, for instance. The dielectric may be provided on a base die or wafer of semiconductor, insulating, or conductive material. The materials of the first substrate may be the same (or similar) material of the second substrate. However, in an alternate embodiment, the materials of the first substrate is a different material than the material of the second substrate. The first surface of the second substrate is bonded to the first surface of the first substrate without an intervening material such as an adhesive.

A first conductive interconnect structure is embedded in the first substrate (or in a layer of the first substrate), a surface of the first conductive interconnect structure being exposed through the first surface of the first substrate to form a first interconnect pad. A second conductive interconnect structure is embedded in the second substrate (or in a layer of the second substrate), a surface of the second conductive interconnect structure being exposed through the first surface of the second substrate to form a second interconnect pad. The first interconnect pad faces, and may contact a portion of the first surface of the first substrate and the second interconnect pad faces, and may contact a portion of the first surface of the second substrate. In one implementation, the second interconnect pad is directly bonded to the first interconnect pad.

In various examples, the second interconnect pad may be misaligned with respect to the first interconnect pad, resulting in some overlap of the first and/or second interconnect pads over the insulating material or dielectric of the opposite substrate.

In the embodiment, a first barrier interface is disposed at the first substrate and at least partially surrounds a perimeter of the first interconnect pad. The first barrier interface comprises a material different from the insulating material or dielectric of the first substrate and is arranged to inhibit a diffusion of a material of the second conductive interconnect structure into the first substrate. In the embodiment, the material of the first barrier interface is also a different material than the material of the second conductive interconnect structure. In one implementation, the first barrier interface comprises an air gap, a roughened surface, or the like.

In another embodiment, the microelectronic assembly also includes a second barrier interface disposed at the second substrate. The second barrier interface at least partially surrounds a perimeter of the second interconnect pad and comprises a material different from the insulating material or dielectric of the second substrate. The second barrier interface is arranged to inhibit a diffusion of a material of the first conductive interconnect structure into the second substrate. In one implementation, the second barrier interface comprises an air gap, a roughened surface, or the like.

In some embodiments, the first and/or second barrier interfaces may comprise multiple materials or may comprise multiple portions comprised of one or more materials. In other embodiments, the first and/or second barrier interfaces may comprise a combination of materials, air gaps, roughened surfaces, and the like.

In various embodiments, the first or second barrier interfaces may partially or fully surround multiple interconnect pads of their respective substrates. Alternatively, multiple barrier interfaces may partially or fully surround one or more interconnect pads of the first or second substrates.

In some embodiments, the first or second barrier interfaces can also mitigate or prevent dielectric erosion (e.g., rounding) that can occur at the perimeter of a conductive interconnect structure during planarization, or the like.

Some of the disclosed processes may be illustrated using block flow diagrams, including graphical flow diagrams and/or textual flow diagrams. The order in which the disclosed processes are described is not intended to be construed as a limitation, and any number of the described process blocks can be combined in any order to implement the processes, or alternate processes. Additionally, individual blocks may be deleted from the processes without departing from the spirit and scope of the subject matter described herein. Furthermore, the disclosed processes can be implemented in any suitable manufacturing or processing apparatus or system, along with any hardware, software, firmware, or a combination thereof, without departing from the scope of the subject matter described herein.

Implementations are explained in more detail below using a plurality of examples. Although various implementations and examples are discussed here and below, further implementations and examples may be possible by combining the features and elements of individual implementations and examples.

DETAILED DESCRIPTION Overview

FIG. 1 is a profile view of a pair of stacked substrates 102 and 104 showing a misalignment of embedded conductive structures 106 and 108 within the stacked substrates 102 and 104, respectively. The substrates 102 and 104 are comprised of an insulating material or dielectric (e.g., silicon oxide, or the like), at least at the bonding surface of each substrate 102 and 104. For example, substrates 102 and 104 can represent the top insulating layer of a microelectronic component comprised of a base layer (of active semiconductor, e.g., silicon, or the like) topped with one or more metallization layers within associated insulating layers. In some cases, substrate 102 may be significantly larger than substrate 104. In one example, substrate 104 may comprise a die having a width between 1 to 30 mm or even larger, while substrate 102 may comprise another die (for example) that is larger than substrate 104, a larger substrate such as a flat panel, a 200 or 300 mm wafer, or the like.

Prior to bonding, the portions of the embedded conductive structures 106 and 108 that are exposed through the bonding surfaces of the substrates 102 and 104 may form interconnect pads, or the like. In an example, the substrates 102 and 104 are bonded at respective bonding surfaces, and the conductive structures 106 and 108 are electrically coupled, and generally are also mechanically bonded to form a single (continuous) conductive structure. The bond-line 110 indicates where the bonding surfaces of the substrates 102 and 104 are joined.

In an example, bonding the substrates 102 and 104 forms a microelectronic assembly 100. For instance, the substrates 102 and 104 may be direct bonded, including using a hybrid bonding technique, without using intervening materials such as adhesives. Prior to bonding, the conductive structures 106 and 108 may be slightly recessed below the surface of the substrates 102 and 104, to prepare for metal expansion. The surfaces of the substrates 102 and 104 are bonded via direct bonding (e.g., via Zibond™), dielectric to dielectric at room temperature without the use of adhesive. Then with high temperature annealing (<350 C), the contact pads 106 and 108 expand and form a metal-to-metal bond creating an electrical connection. After the bonding operations, for example when the substrates 102 and 104 comprise wafers, the bonded assembly 100 may be tested for known good dies prior to segmentation, to separate into various bonded substrates or dies.

As shown in FIG. 1, due to one or more of various reasons discussed above, including the inaccuracy (or tolerance) of the pick-and-place tool used to bond substrate 104 to substrate 102, the conductive structures 106 and 108 may be misaligned when the substrates 102 and 104 are placed together and bonded. The offset 112 of the misalignment comprises an overlap of the interconnect pad 106 beyond a perimeter or edge of the interconnect pad 108 and/or an overlap of the interconnect pad 108 beyond the perimeter or edge of the interconnect pad 106. Due to the offset 112, a portion of one or both of conductive structures 106 and 108 may contact the insulating material of substrates 104 and 102 respectively. As discussed above, the conductive material (e.g., copper or a copper alloy, etc.) of one or both of the conductive structures 106 and 108 may diffuse into the insulating material or dielectric of the substrates 104 and 102 due to this contact. Additionally, some process elements (such as high temperature annealing, for instance) or operational parameters (e.g. high frequency electric field, etc.) can exacerbate the diffusion of the conductive material into the insulating material or dielectric of the substrates 104 and 102 inducing undesirable leakage in the dielectric layer for example.

FIG. 2 is a graphical flow diagram illustrating an example process 200 of forming a microelectronic assembly 100 comprising a pair of substrates 102 and 104 with embedded conductive structures 106 and 108, according to an embodiment. In an example, a damascene structure is formed from a substrate 102. At block (A), a conductive material 202 (e.g., copper, a copper alloy, nickel or nickel bearing conductor, or the like) is deposited over a surface of the substrate 102, including into the damascene cavity, filling the cavity. At block (B), the conductive material 202 is planarized (e.g., via chemical mechanical polishing (CMP), etching, etc.) to form the conductive structure 106. The exposed portion of the conductive structure 106 may comprise an interconnect pad 204. In one embodiment it may be preferable that the interconnect pad 204 be slightly recessed below the bonding surface of the substrate 102. The bonding surface is prepared by cleaning methods to remove defects inducing undesirable particles, residual organic material and their likes. The cleaned surface or surfaces may be prepared by exposing one or more of the surfaces to nitrogen plasma in preparation for the bonding process.

At block (C), a similar damascene structure is formed from another substrate 104, which, after planarization, includes a conductive structure 108. The exposed portion of the conductive structure 108 may comprise an interconnect pad 206. The prepared bonding surface of the substrate 104 is placed over and stacked onto the substrate 102 in preparation for bonding. The assembled substrates 102 and 104 are then thermally treated at a temperature below 350° C. and preferably below 250° C., for enough time for the bonding surfaces to bond permanently and for the opposing conductive materials to couple both mechanically and electrically.

Blocks (D), (E), and (F) show three potential outcomes of bonding substrate 102 to substrate 104. Block (D) represents an ideal scenario, where the conductive structures 106 and 108 are aligned well, without offset. Block (E) represents an average scenario where there is an average misalignment of the conductive structures 106 and 108, based on an average inaccuracy (e.g., tolerance) of the placement tool used to bond the substrate 104 to the substrate 102. Block (F) represents an extreme scenario where there is an extreme misalignment of the conductive structures 106 and 108, based on a maximum inaccuracy (e.g., tolerance) of the placement tool used to bond the substrate 104 to the substrate 102. Typically, the higher placement speed of the pick and place tool, the lower is its placement accuracy, i.e. larger the offset. For applications with extremely small interconnect pad sizes, the placement tool can slow down dramatically to improve the placement accuracy, which affects throughput.

As discussed above, the offset 112 (shown at blocks (E) and (F)) provides an opportunity for diffusion of the conductive materials of conductive structures 106 and 108 into the insulating material or dielectric of substrates 104 and 102, respectively.

Example Barrier Interface

According to this disclosure, to avoid the diffusion of copper into oxide, for instance, a barrier interface 302 comprising a dielectric bonding layer, conductive barrier layer, or other barrier can be applied around the interconnect pads 106 and/or 108 to form a barrier against diffusion. The barrier interface 302 material is selected such that the diffusivity of the conductive materials of conductive structures 106 and 108 (copper, for instance) into the barrier materials is worse as compared to that of the insulating material or dielectric of the substrates 104 and 102 (e.g., silicon oxide). In various embodiments, the barrier materials may include conductive or non-conductive materials with preselected diffusivity characteristics.

FIGS. 3A and 3B are profile views showing examples of a barrier interface 302 employed with stacked substrates 102 and 104 having embedded conductive structures 106 and 108, according to various embodiments. In an implementation, the substrates 102 and 104 are directly bonded without an intervening material such as an adhesive, to form a microelectronic assembly 300. In the implementation, the microelectronic assembly 300 comprises a microelectronic assembly 100 as discussed above and includes one or more barrier interfaces 302 on one or both of the substrates 102 and 104. In an alternate implementation, the microelectronic assembly 300 includes more than two substrates (such as substrates 102 and 104) in the bonded stack, with one or more of the substrates of the stack including one or more barrier interfaces 302. In another implementation, the microelectronic assembly 300 includes two or more substrates (such as substrates 102 and 104) bonded separately to another substrate or a wafer, with two or more of the substrates including one or more barrier interfaces 302.

In an implementation, the barrier interface(s) 302 of the assembly 300 are disposed at one or both of the substrates 102 and 104, and at least partially surround a perimeter of the interconnect pads 204 and/or 206, and/or the embedded conductive structures 106 and 108, respectively. As shown at FIG. 3A, the barrier interface(s) 302 may comprise one or more materials different from the insulating material or dielectric of the substrate 102 and/or the substrate 104. For example, the barrier interface(s) 302 may comprise a dielectric material different from the insulating material or dielectric of the substrate 102 and/or the substrate 104. In various implementations, the barrier interface(s) 302 comprise one or more of silicon nitride, silicon oxynitride, silicon carbide, silicon carbonitride, diamond, boron doped glass or oxide, aluminum oxide, or a like diffusion resistant material. In other implementations, the barrier interface(s) 302 comprise nickel, a nickel alloy, or one or more other conductive materials in various combinations.

Additionally, employing a barrier interface 302 can include techniques to prevent diffusion by avoiding bonding at the relevant bonding interface. For example, in various embodiments, the respective conductive interconnect structures 106 and 108 may be bonded, but little or none of the immediately surrounding insulating material or dielectric is bonded. As shown at FIG. 3B, one or more of the barrier interface(s) 302 may comprise a recess, an air gap, or a gas-filled cavity, or the like. Again, the barrier interface(s) 302 comprise a different material from the insulating material or dielectric of the substrate 102 and/or the substrate 104. In various implementations, the barrier interface(s) 302 comprise an inert gas or fluid, a preselected gas or fluid (based on desired properties), vacuum, or the like. The air gap barrier interface 302 may be formed by etching, making undercuts in the substrate 102 and/or 104, dishing the substrate 102 and/or 104 via CMP, grinding, substrate rounding near substrate and interconnect pad interface during CMP, or the like, and so forth.

Referring to FIGS. 3A and 3B, in the implementations, the barrier interface(s) 302 are arranged to inhibit a diffusion of the material of the conductive interconnect structures 106 and 108 into the substrates 104 and 102, respectively. For example, the material of the barrier interface(s) 302 is selected such that a diffusivity of the material of the conductive interconnect structure 106 or a diffusivity of the material of the conductive interconnect structure 108 into the material of the barrier interface(s) 302 of the substrate 104 or the substrate 102 is less than a diffusivity of the material of the conductive interconnect structures 106 or 108 into the material of the substrate 104 or the substrate 102 (e.g., silicon oxide).

In various embodiments, one or more of the barrier interfaces 302 can be arranged to fully surround or encompass the conductive structures 106 and/or 108 and/or their respective interconnect pads 204 and/or 206 (i.e., the mating surface of the conductive structures 106 and 108, respectively), or to partially surround the conductive structures 106 and/or 108 and/or their respective interconnect pads 204 and/or 206, forming a barrier against the diffusion of the conductive material (e.g., copper) into the material (e.g., silicon oxide) of the substrates 102 and 104.

As shown in FIGS. 3A and 3B, in various embodiments, a barrier interface 302 has a thickness (i.e., width, extent, etc.) 304 that is greater than the placement accuracy 306 of the pick-and-place tool (also represented by the overlap 112 in FIG. 1). This thickness of the barrier interface 302 ensures that the material of the conductive structures 106 and 108 will contact the barrier interface 302 rather than the substrate 104 or 102 in case of maximum placement misalignment. This ensures that any conductive material overlap occurs at the barrier interface 302, and not at the substrate material (e.g., silicon oxide), thus preventing diffusion. Additionally, this significantly relaxes the placement accuracy requirements of the pick and place tool, which can improve the throughput, especially in a die to die and die to wafer bonding process.

Accordingly, in one embodiment, a relative lateral displacement of one interconnect pad 204 (of conductive structure 106) to the other interconnect pad 206 (of conductive structure 108) is less than a width of one or more of the barrier interfaces 302. Further, in one implementation, a width of one or more of the barrier interfaces 302 is at least 10% of a diameter of the interconnect pads 204 and/or 206 of the conductive structures 106 and/or 108. In other implementations, the width of one or more of the barrier interfaces is at least 20% of the diameter of the interconnect pads 204 and/or 206.

As shown in FIG. 3B, in some embodiments, at least some portion of the pad 204 extends or protrudes beyond a recessed surface of the insulating material of the substrate 102 on the microelectronic assembly 300 after bonding, and may extend beyond the bond line 110. This extension may be a result of forming the barrier interface 302, it may be the result of dielectric erosion (i.e., rounding) on the surface of the substrate 102 around the periphery of pad 204 from planarizing, or both, or the result of other causes separately or in combination. A like extension or protrusion of at least some portion of the pad 206 past the recessed surface of the substrate 104 after bonding, and perhaps an extension past the bond line 110, may also be present in the embodiments.

In any case, a result of the extension of the pad 204 and/or the pad 206 is an air gap at least partially surrounding the pad 204 and/or the pad 206 (intentional or otherwise). In some cases, when the interconnect pads 204 and 206 are misaligned (as shown in FIG. 3B), only a partial extension or protrusion of at least some portion of the pad 204 or 206 past the bond line 110, may be present in some embodiments.

In FIG. 3A, a relative lateral displacement of one interconnect pad 204 (of conductive structure 106) to the other interconnect pad 206 (of conductive structure 108) is less than a width of one or more of the barrier interfaces 302. During the annealing process, as the conductive pads 204/206 expand more than the substrate material 102/104 and the barrier interface material 302, this high mismatch between the coefficients of thermal expansion may induce debonding of the portion of substrate 102 from the substrate 104 at the location as the pads 204/206 push the barrier interface 302. In an implementation, the debonding may be mitigated (e.g., reduced or eliminated) by adjusting the annealing times and temperatures. In the implementation, the bonding surfaces may be heat treated at around 100-150° C. for 2 to 4 hours to form a strong bond between the substrates 102 and 104. The pads 204 and 206 may then be annealed during a second heat treatment using a pulse anneal technique at approximately 250-400° C. for 10 seconds to less than 300 seconds. In an example, the pulse anneal times for the second heat treatment are less than 10% of the heating time for the first heat treatment. In the implementation, the adjusted heating/annealing times are effective to reduce or eliminate the mismatch stress or load of the bonded microelectronic assembly 300.

While FIGS. 3A and 3B show conductive structures extending through substrates 102 and 104, the structures may extend partially through the substrate or layers on the substrate. Specific details of the conductive connections on, in, or though the substrate are not shown in FIGS. 3-7 for simplicity and in order to focus on the structures, or portions of the structure, at the bond interface.

FIGS. 4A-4E are profile views showing additional example barrier interfaces 302 employed with stacked substrates 102 and 104 having embedded conductive structures 106 and 108, according to additional embodiments. As shown at FIGS. 3A and 4A, a barrier interface 302 may be embedded into one or more of the substrates 102 and/or 104. In an embodiment, as shown in FIGS. 3A and 4A, one or more barrier interfaces 302 is embedded in a substrate 102 and/or 104 and extends into the substrate 102 and/or 104 to a depth less than or equal to a depth of a conductive structure 106 or 108. In this configuration, the substrates 102 and 104 are protected from conductive material diffusion. In an embodiment, as shown at FIGS. 3A and 4A, the barrier interface 302 may be disposed (and may be exposed) at the bonding surface of a substrate 102 and/or 104, and may extend a predetermined depth into the substrate 102 and/or 104.

As shown in FIG. 4B, a barrier interface 302 may be used on one of the substrates 102 or 104 when conductive structures 106 and 108 are dissimilar sizes. For example, the barrier interface 302 (at an advantageous thickness) may be used on the smaller of the conductive structures 106 and 108, to protect for diffusion from the larger of the conductive structures 106 and 108, with no exposed overlap onto the substrates 102 or 104. For instance, in an embodiment, the width of the first interconnect pad 106 is less than the width of the second interconnect pad 108, and the barrier interface 302 is disposed at the first substrate 102, at least partially surrounding the perimeter of the first interconnect pad 106. The barrier interface 302 thickness/width is such that the combined width of the first interconnect pad 106 and the barrier interface 302 is greater than the width of the second interconnect pad 108. In other words, as with each of the embodiments, at least one of the perimeter edges of the second interconnect pad 108 is within the perimeter of the barrier interface 302. The other perimeter edge of the second interconnect pad 108 is also within the perimeter of the barrier interface 302 or within the perimeter of the first interconnect pad 106 (preventing diffusion into substrate material).

As shown in FIG. 4C, an embedded barrier interface 302 may or may not be exposed at the bonding surface of the substrates 102 and 104. The barrier interface 302 may be disposed a preselected distance below the bonding surface, and may have various depth and thickness (i.e., width or extents). For example, in one embodiment, the barrier interface 302 can extend across the width of the substrate 102 or 104. The barrier interface 302 can abut the conductive structures 106 and/or 108, and diffusion may be limited to the area of the substrates 102 and 104 above the barrier interface 302, the barrier interface 302 preventing diffusion below the barrier interface 302. In some embodiments, such a barrier interface 302 may be comprised of a polymeric layer, or like material with a desired diffusivity characteristic.

As shown in FIG. 4D, the barrier interface 302 may comprise a rough area of the bonding surface of the substrate 102 and/or 104, which may include one or more gaps in the bond between the substrates 102 and 104 at a predetermined width. For instance, a highly planar bonding surface with low variance in topology is generally prepared on both substrates 102 and 104 in order to have a reliable direct bond between the substrates 102 and 104. In an embodiment, however, the surface area of the substrates 102 and/or 104 partially or fully around the conductive structures 106 and/or 108 may have a higher roughness (greater variance in surface topology) to create uneven or irregular surfaces between the substrates 102 and 104, to reduce or eliminate the bond at that area of the substrates 102 and 104. For example, the roughness can make the surface insufficiently smooth (or leave not enough surface contact) to form a bond. The high roughness (e.g., greater than 10 nm variance) barrier interface 302 can be formed with etching, cutting, grinding, selective CMP, or the like.

Similarly to the embodiment described with regard to FIG. 4B, as shown at FIG. 4E, the barrier interface 302 may be used on one of the substrates 102 and 104 when the conductive structures 106 and 108 are dissimilar sizes. In the case of FIG. 4E, the barrier interface 302 comprises an air gap (or a fluid-filled gap) used with the smaller of the conductive structures 106 and 108. When the barrier interface 302 is sized advantageously, there is no overlap of conductive material onto the substrates 102 or 104, and thus no diffusion. For instance the air-gap barrier interface 302 may be sized so that any offset between the interconnect pads 204 and 206, effectively the edges of the interconnect pads 204 and 206, falls within the barrier interface 302 and not at the material of the substrates 102 and 104.

In an implementation, one or more barrier interfaces 302 comprises a combination including two or more of: a plurality of air gaps, one or more materials different from the insulating or dielectric material of the substrates 102 and 104, and a roughened surface of a predetermined width.

As shown in the plan view of FIG. 4F, in an embodiment, a plurality of conductive structures 106 (or interconnect pads 204) may be partially or fully surrounded or encompassed by a single barrier interface 302. In such an embodiment, the substrate 102 may be bonded to another substrate 104 having a plurality of conductive structures 108, or more than one substrate with conductive structures.

Alternately, multiple barrier interfaces 302 may partially or fully surround one or more conductive structures 106, 108 or interconnect pads 204, 206 of one or more of the substrates 102 and 104. For example, as shown in FIGS. 5A-5C, multiple conductive structures 106 and 108 are partially or fully surrounded by barrier interfaces 302. For instance, in an embodiment, a plurality of additional conductive interconnect structures 106 are embedded in the substrate 102, where a surface of each of the additional conductive interconnect structures 106 is exposed through the bonding surface of the substrate 102 to form a plurality of additional interconnect pads 204. A plurality of additional conductive interconnect structures 108 are embedded in the opposite substrate 104, and a surface of each of the additional conductive interconnect structures 108 is exposed through the bonding surface of the substrate 104 to form a plurality of additional interconnect pads 206.

A barrier interface 302 at least partially surrounds at least a subset of the group of pads including the first interconnect pad 106 and the plurality of additional interconnect pads 106. The barrier interface 302 is arranged to inhibit diffusion of the conductive material of the group of interconnect structures including the conductive interconnect structure 108 and the plurality of additional conductive interconnect structures 108 into the substrate 102, based on the position and the composition of the barrier interface 302. Further, the barrier interface(s) 302 may also be arranged to inhibit diffusion of the conductive material of the group of interconnect structures including the conductive interconnect structure 106 and the plurality of additional conductive interconnect structures 106 into the substrate 104.

As shown in FIGS. 5A and 5C, each of multiple conductive structures 106 and 108 may include a barrier interface 302. For instance, in an embodiment, one or more additional barrier interfaces 302 are disposed at the substrate 102 and/or the substrate 104 that at least partially surround a perimeter of one or more additional subsets of the first interconnect pad 106 and the plurality of additional interconnect pads 106, and/or the second interconnect pad 108 and the plurality of additional interconnect pads 108. The one or more additional barrier interfaces 302 comprise a material different from the insulating material or dielectric of the substrate 102 and/or the substrate 104, and are arranged to inhibit diffusion of the material of the group of interconnect structures including the conductive interconnect structure 108 and the plurality of additional conductive interconnect structures 108 into the material of the substrate 102, based on the position and the composition of the barrier interfaces 302. Further, the one or more additional barrier interfaces 302 can be arranged to inhibit diffusion of the material of the group of interconnect structures including the conductive interconnect structure 106 and the plurality of additional conductive interconnect structures 106 into the material of the substrate 104.

Referring to FIGS. 5A-5C, in some embodiments, between each barrier interface 302 may be a gap 502, which may be a space between the barrier interfaces 302, a gas-filled gap, or the like. The gap 502 forms a physical separation between the bonding surfaces of the substrates 102 and 104, at least around the periphery of the conductive structures 106 and/or 108. In some embodiments, the combination of the barrier interfaces 302 and the gap(s) 502 prevent or reduce diffusion of the conductive material of the conductive structures 106 and/or 108, and their respective interconnect pads 204 and 206, into the material of the substrates 104 and 102. In another embodiment, no such gap 502 is formed between the bonding surfaces of the substrates 102 and 104.

Alternately, as shown in FIG. 5B, single conductive structures 106 and/or 108, as well as groups of two or more conductive structures 106 and/or 108 may be partially or fully surrounded by single barrier interfaces 302. Between barrier interfaces 302 there may or may not be a gap 502, as described above. A via (e.g., TSV), such as the via 504 may be present in any of the embodiments discussed herein, including the example embodiment shown at FIG. 5B. The via 504 may extend to the outer extents (e.g., exposed surfaces) of one or both of the substrates 102 and 104 (and beyond), or it may extend some fractional portion through the substrate 102 and/or the substrate 104.

Example Processes

FIG. 6 is a graphical flow diagram illustrating an example process 600 of forming a microelectronic assembly 300 comprising a pair of substrates 102 and 104 with embedded conductive structures 106 and 108 and one or more barrier interfaces 302, according to an embodiment.

At block A, the method includes forming a cavity 602 (or a plurality of cavities 602 and 603) in a surface of the substrate 102. The cavities 602 and 603 may be formed by patterned etching, or the like. In an embodiment, one of the cavities 603 may extend to a depth of less than 5% of a depth of the other cavity 602. At block B, a barrier layer 604 is formed on the surface of the substrate 102 and within the cavity 602. The barrier layer 604 may be comprised of silicon nitride, silicon oxynitride, silicon carbide, silicon carbonitride, diamond, boron doped glass or oxide, aluminum oxide, or other suitable material with worse diffusivity properties than silicon oxide, or a combination thereof, for instance. In other embodiments, the barrier layer 604 may comprise a conductive material, for example titanium or tantalum or their corresponding nitrides, nickel and nickel alloys, or other conductive materials and combinations.

At block C, the cavity 602 coated with the barrier layer 604 is filled with the conductive material 202, such as copper, a copper alloy, or the like. This could be done using a duel damascene process, for instance. In some examples it may be desirable for the conductive structure 106 to contact the bottom of the cavity 602, at the substrate 102 rather than the barrier layer 604. In these examples, portions of the barrier layer 604 may be removed from the bottom portion (and/or any other desired portion) of the cavity 602 to expose the substrate 102 prior to filling the cavity 602 with the conductive material 202.

At block D, overflow conductive material 202 is removed, by etching, CMP, or the like, stopping at the barrier layer 604, to form a conductive structure 106 (or multiple conductive structures 106) within the barrier layer 604. At block E, the conductive structure 106 and part of the barrier layer 604 are planarized via CMP, for example, to form a barrier interface 302 partly or fully surrounding an interconnect pad 204, which may have a very small recess, and a substantially planar surface (having a smooth surface topography with a variance of no more than 10-20 nm) of the substrate 102.

In some embodiments, the barrier layer 604 or barrier interface 302 is useful to prevent or to mitigate erosion of the insulating material or dielectric of the substrate 102 (e.g., rounding) that can occur during planarization. For instance, the barrier layer 604 may extend a predetermined extent (i.e., width, diameter, etc.) beyond the conductive structure 106 and over the surface of the substrate 102, protecting the surface of the substrate 102 during planarization. In other words, the first barrier interface 302 is disposed over at least a portion of the substantially planar surface of the first substrate 102, and is arranged to protect the substantially planar surface from erosion due to planarization or polishing of the substantially planar surface. With the barrier interface 302 in place, no dielectric erosion (e.g., rounding) may occur at the intersection of the conductive structure 106 and the substrate 102, or at the intersection of the barrier interface 302 and the substrate 102. In some examples, the barrier interface 302 may be used as an indicator for polishing the substrate 102, and in some examples the barrier interface 302 may be polished a desired amount as well to achieve a flat, smooth bonding surface.

At block F, a like microelectronic structure, with prepared substrate 104, conductive structure 108, and barrier layer 302 is placed onto the substrate 102 for bonding. At block G, the substrate 104 is direct bonded to the substrate 102 without an intervening material, such as adhesive, to form the microelectronic assembly 300. In particular, the substrate 104 is bonded to the bonding surface of the substrate 102 and to the barrier layer 302 on the substrate 102, and the substrate 102 is bonded to the bonding surface of the substrate 104 and to the barrier layer 302 on the substrate 104. At this step, the conductive structures 106 from the substrate 102 and the conductive structures 108 from the substrate 104 can be slightly recessed below the bond-line 110 due to CMP process and may not be in physical contact. In some cases, the conductive structure 108 may be bonded to the conductive structure 106 via heated annealing, or the like. After annealing at high temperature as discussed earlier, the conductive structure 108 is mated to the conductive structure 106 to form electrical connectivity.

Any offset of the conductive structure 106 to the conductive structure 108 due to misalignment rests on the barrier interface 302 rather than on the substrates 102 and 104. Accordingly, diffusion of conductive material (e.g., copper) into substrate 102 and/or 104 material (e.g., silicon oxide) is reduced or eliminated due to the barrier interface(s) 302.

In another embodiment, after planarization at block E of FIG. 6, an additional layer, typically of the same type of material as the substrate 102, e.g. silicon oxide, is deposited over the interconnect pad 204 and the barrier layer 302. This is followed by another planarization process, e.g. CMP, to remove excess substrate material and to achieve a surface in which the barrier layer 302 is flush with the surface of the substrate 102 surrounding it. The barrier layer 302 partially or fully surrounds the interconnect 204 and the substrate layer 102 fully or partially surrounds the barrier layer 302. In the embodiment, during block G, the direct bonding of the bonding layers of 102 and 104 occurs along with the direct bonding of the barrier layer 302 of the substrate 102 with the barrier layer 302 of the substrate 104. This is followed by the annealing step, wherein the conductive structure 108 may be bonded to the conductive structure 106 via heated annealing, or the like.

FIG. 7 is a graphical flow diagram illustrating an example process 700 of forming a microelectronic assembly 300 comprising a pair of substrates 102 and 104 with embedded conductive structures 106 and 108 and one or more barrier interfaces 302, according to another embodiment.

At block A, the method includes depositing the barrier layer material 604 onto the surface of an oxide or other dielectric (for example) substrate 102. At block B, a portion of the barrier layer 604 and a portion of the dielectric of the substrate 102 are removed, and the resulting cavity 602 is filled with a conductive material 202 (at block C). In some embodiments, the process of forming the conductive material 202 in the cavity 602 may include coating a second barrier (not shown) over the surface of the first barrier layer 604 and the cavity 602 before filling the cavity 602 with the conductive material 202.

At block D, a conductive structure 106 with interconnect pad 204 surrounded by a barrier interface 302 is formed by planarizing the conductive material 202, and the second barrier layer if present. In an implementation, the barrier interface 302 is efficacious to prevent dielectric erosion of the substrate 102 at the intersection of the conductive structure 106 during the planarizing. In an embodiment, this structure 102 with prepared barrier interface 302 and conductive structure 106 may be bonded to another like structure, but without the barrier interface 302 on the other structure. In such an embodiment, the barrier layer 302 can act as a bonding surface for the other structure, based on the material used for the barrier layer (e.g., silicon nitride, or the like).

At block E, if desired, the barrier interface 302 can be altered to remove any unwanted portions. A resist, mask, or other pattern 702 may be deposited, and the barrier interface 302 etched as desired (at block F). Additional substrate material (such as silicon oxide, for example) can be deposited onto the surface of the substrate 102 to prepare the surface for bonding. For instance, the added material may be deposited while the mask 702 is still in place, or after removing the mask 702. The surface of the substrate 102 is then planarized (via CMP, or the like) to achieve a flat, smooth surface including the surface of the substrate 102 flush with the barrier interface 302, in preparation for bonding.

At block G, a prepared substrate 102 is shown with an interconnect pad 204 having a partially or fully encompassing barrier interface 302. Two similarly prepared substrates 102 and 104 may be stacked and bonded at their planarized surfaces to form a microelectronic structure 300, as shown at block H. Any overlap of conductive material occurs at the barrier interface(s) 302 rather than at the dielectric of the substrates 102 and/or 104. This method can also be used to form multiple conductive interconnect structures 106, 108 with barrier interface(s) 302 partially or fully surrounding the multiple conductive interconnect structures 106, 108.

In an alternative implementation, the conductive structures 106 and/or 108 may include conductive mechanical pads. In the implementation, the mechanical pads mate intimately with the barrier layer 302 or the substrate 102/104 to secure the mechanical pads to the substrate 102/104.

FIG. 8 is a flow diagram describing an example process 800 of forming a microelectronic assembly (such as the microelectronic assembly 300) comprising a pair of substrates (such as the pair of substrates 102 and 104) with embedded conductive structures (such as conductive structures 106 and 108) and one or more barrier interfaces (such as barrier interface 302), according to an embodiment.

At block 802, the process includes forming a first cavity (or a plurality of first cavities) in a surface of a first substrate (such as substrate 102, for example). In an embodiment, the first substrate comprises an insulating material or dielectric, such as silicon oxide, or the like, which may be provided on a semiconductor base having circuitry on, in, through the base. At block 804, the process includes forming a first barrier interface (such as barrier interface 302, for example) at the first substrate and at least partially surrounding a perimeter of the first cavity. In an implementation, the process includes depositing a first barrier layer material onto at least a portion of a surface of the first cavity. The first barrier layer material may also be deposited onto at least a portion of the surface of the first substrate, particularly, partially or fully surrounding the first cavity. In an embodiment, the first barrier interface comprises a material different from the insulating material or dielectric and is arranged to inhibit a diffusion of a conductive material into the first substrate.

At block 806, the process includes filling the first cavity with the conductive material. In various embodiments, the conductive material comprises copper, a copper alloy, or like conductive material.

At block 808, the process includes planarizing at least a portion of the surface of the first substrate, the first barrier interface (including the first barrier layer material), and the conductive material to form a first conductive interconnect structure with a first barrier interface at least partially surrounding an exposed surface of the first conductive interconnect structure. In an embodiment, the first barrier interface is formed to have a predetermined width.

In an alternate implementation, the process includes depositing an additional layer of insulating material or dielectric (e.g., silicon oxide) onto the surface of the first substrate to improve the bonding surface of the substrate. For instance, the depositing may be used to fill any voids created during previous planarization steps, to flush the surface of the substrate with the barrier interface, or the like. In the implementation, the surface of the substrate is re-planarized after the depositing to form a flat, smooth, and flush bonding surface. The first barrier interface surrounds (at least partially) the conductive interconnect, and the insulating material or dielectric surrounds (at least partially) the first barrier interface.

In an implementation, the process includes forming a second cavity in a surface of a second substrate (such as substrate 104, for example), where the second substrate also comprises an insulating material or dielectric. The process includes forming a second barrier interface at the second substrate and at least partially surrounding a perimeter of the second cavity, where the second barrier interface comprises a material different from the insulating material or dielectric of the second substrate. In an implementation, the process includes depositing a second barrier layer material onto at least a portion of the surface of the second substrate and onto at least a portion of a surface of the second cavity.

The second barrier interface is arranged to inhibit a diffusion of the conductive material of the first conductive structure (embedded in the first substrate) into the second substrate. In an implementation, the process includes forming the first barrier interface and/or the second barrier interface to comprise a gas-filled gap. In another implementation, the process includes forming the first barrier interface and/or the second barrier interface to comprise a roughened area of the surface of the first substrate and/or the second substrate that inhibits bonding at the roughened area. In other embodiments, the first barrier interface and/or the second barrier interface comprises one or more of silicon nitride, silicon oxynitride, silicon carbide, silicon carbonitride, diamond, boron doped glass or oxide, aluminum oxide, or a like diffusion resistant material.

In the implementation, the process includes filling the second cavity with the conductive material and planarizing at least a portion of the surface of the second substrate, the second barrier interface, and the conductive material at the second substrate to form a second conductive interconnect structure (such as the conductive structure 108, for example) with a second barrier interface at least partly surrounding an exposed surface of the second conductive interconnect structure. In one example, the process includes forming the first barrier interface or the second barrier interface to have a width that is at least 10% of a diameter of the second conductive interconnect structure. In another example, the process includes forming the first barrier interface or the second barrier interface to have a width that is at least 20% of a diameter/width of the second conductive interconnect structure.

The process further includes directly bonding the surface of the second substrate to the surface of the first substrate without an adhesive material and mating the second conductive interconnect structure to the first conductive interconnect structure, such that any portion of the second conductive interconnect structure contacts the first barrier interface and not the first substrate and any portion of the first conductive interconnect structure contacts the second barrier interface and not the second substrate when the second conductive interconnect structure and the first conductive interconnect structure are offset or misaligned.

In an implementation, the process includes directly bonding the exposed surface of the second conductive interconnect structure to the exposed surface of the first conductive interconnect structure. In an example, the process includes high temperature annealing to bond the conductive structures into a single conductive interconnect.

Although various implementations and examples are discussed herein, further implementations and examples may be possible by combining the features and elements of individual implementations and examples.

CONCLUSION

Although the implementations of the disclosure have been described in language specific to structural features and/or methodological acts, it is to be understood that the implementations are not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as representative forms of implementing example devices and techniques.

Each claim of this document constitutes a separate embodiment, and embodiments that combine different claims and/or different embodiments are within the scope of the disclosure and will be apparent to those of ordinary skill in the art upon reviewing this disclosure. 

What is claimed is:
 1. A microelectronic assembly, comprising: a first substrate having a first substantially planar surface, the first substrate comprising an insulating material; a second substrate having a first substantially planar surface, the second substrate comprising an insulating material, the first surface of the second substrate directly bonded to the first surface of the first substrate without an adhesive; a first conductive interconnect structure embedded in the first substrate, a surface of the first conductive interconnect structure being exposed through the first surface of the first substrate to form a first interconnect pad; a second conductive interconnect structure embedded in the second substrate, a surface of the second conductive interconnect structure being exposed through the first surface of the second substrate to form a second interconnect pad; and a first barrier interface disposed at the first substantially planar surface of the first substrate and at least partially surrounding a perimeter of the first interconnect pad thereby separating the first conductive interconnect structure from the insulating material at the first substantially planar surface, the first barrier interface comprising a material different from the insulating material of the first substrate, at least a portion of the first barrier interface extending a predetermined depth into the first substrate, the predetermined depth being less than a depth of the first conductive interconnect structure.
 2. The microelectronic assembly of claim 1, wherein the first barrier interface is arranged to inhibit a diffusion of a material of the second conductive interconnect structure into the first substrate.
 3. The microelectronic assembly of claim 1, wherein the first barrier interface is comprised of a conductive material.
 4. The microelectronic assembly of claim 3, wherein the first barrier interface is comprised of cobalt, titanium nitride, tantalum nitride, nickel or a nickel alloy.
 5. The microelectronic assembly of claim 1, wherein the first barrier interface is a single layer that comprises: a first portion that extends a predetermined depth into the first substrate, the predetermined depth being less than a depth of the first conductive interconnect structure, and a second portion that extends from the first portion and along the surface of the first conductive interconnect structure.
 6. The microelectronic assembly of claim 1, wherein the first barrier interface is disposed over at least a portion of the first substantially planar surface of the first substrate, and is arranged to protect the first substantially planar surface from erosion due to planarization or polishing of the first substantially planar surface.
 7. The microelectronic assembly of claim 1, further comprising a second barrier interface disposed at the second substrate and at least partially surrounding a perimeter of the second interconnect pad, the second barrier interface comprising a material different from the insulating material of the second substrate.
 8. The microelectronic assembly of claim 7, where in the second barrier interface is arranged to inhibit a diffusion of a material of the first conductive interconnect structure into the second substrate.
 9. The microelectronic assembly of claim 7, wherein a diffusivity of the material of the first conductive interconnect structure or a diffusivity of the material of the second conductive interconnect structure into the material of the first barrier interface or the material of the second barrier interface is less than a diffusivity of the material of the first conductive interconnect structure or a diffusivity of the material of the second conductive interconnect structure into the material of the first substrate or the material of the second substrate.
 10. The microelectronic assembly of claim 1, wherein the material of the first substrate or the material of the second substrate comprises silicon oxide.
 11. The microelectronic assembly of claim 1, further comprising: a plurality of additional first conductive interconnect structures embedded in the first substrate, a surface of each of the additional first conductive interconnect structures being exposed through the first surface of the first substrate to form a plurality of additional first interconnect pads; a plurality of additional second conductive interconnect structures embedded in the second substrate, a surface of each of the additional second conductive interconnect structures being exposed through the first surface of the second substrate to form a plurality of additional second interconnect pads; and wherein the first barrier interface at least partially surrounds at least a subset of the first interconnect pad and the plurality of additional first interconnect pads.
 12. The microelectronic assembly of claim 11, wherein the first barrier interface is arranged to inhibit a diffusion of a material of the second conductive interconnect structure and the plurality of additional second conductive interconnect structures into the first substrate.
 13. The microelectronic assembly of claim 11, further comprising one or more additional barrier interfaces disposed at the first substrate and at least partially surrounding a perimeter of one or more additional subsets of the first interconnect pad and the plurality of first interconnect pads, the one or more additional barrier interfaces comprising a material different from the insulating material of the first substrate.
 14. The microelectronic assembly of claim 13, wherein the one or more additional barrier interfaces are arranged to inhibit a diffusion of the material of the second conductive interconnect structure and the plurality of second conductive interconnect structures into the first substrate.
 15. The microelectronic assembly of claim 1, wherein the second interconnect pad is bonded to the first interconnect pad to form a single conductive structure.
 16. The microelectronic assembly of claim 1, wherein the second interconnect pad is misaligned with respect to the first interconnect pad, resulting in an overlap of the first interconnect pad beyond a perimeter of the second interconnect pad and/or an overlap of the second interconnect pad beyond the perimeter of the first interconnect pad.
 17. The microelectronic assembly of claim 1, wherein a width of the first interconnect pad is less than a width of the second interconnect pad, the first barrier interface disposed at the first substrate and at least partially surrounding the perimeter of the first interconnect pad, such that the combined width of the first interconnect pad and the first barrier interface is greater than the width of the second interconnect pad.
 18. The microelectronic assembly of claim 1, wherein a perimeter edge of the second interconnect pad is within a perimeter of the first barrier interface.
 19. The microelectronic assembly of claim 1, wherein the insulating material of the first substrate comprises silicon oxide material and the material of the second conductive interconnect structure comprises copper or a copper alloy.
 20. The microelectronic assembly of claim 1, wherein the first barrier interface comprises a dielectric material different from the insulating material of the second substrate.
 21. The microelectronic assembly of claim 1, wherein the first barrier interface is a single layer that comprises: a first portion that extends along the first substantially planar surface a first width from the first conductive interconnect structure, and a second portion below the first substantially planar surface, the second portion extending a second width from the first conductive interconnect structure, the second width being less than the first width.
 22. The microelectronic assembly of claim 1, wherein the first barrier interface is comprised of one or more of silicon nitride, silicon oxynitride, silicon carbide, silicon carbonitride, diamond, boron doped glass or oxide, or aluminum oxide.
 23. The microelectronic assembly of claim 1, wherein a width of the first barrier interface is at least 10% of a diameter of the second interconnect pad and the first barrier interface has a side surface contacting the first conductive interconnect structure and a bottom surface contacting the insulating material of the first substrate.
 24. The microelectronic assembly of claim 1, wherein a width of the first barrier interface is at least 20% of a diameter of the second interconnect pad.
 25. The microelectronic assembly of claim 1, wherein a relative lateral displacement of the first interconnect pad to the second interconnect pad is less than a width of the first barrier interface.
 26. The microelectronic assembly of claim 1, wherein the first barrier interface is embedded in the first substrate and extends into the first substrate to a depth less than or equal to a length of the first conductive structure.
 27. The microelectronic assembly of claim 1, wherein the second interconnect pad is misaligned with respect to the first interconnect pad an offset based on an average inaccuracy of a placement tool used to bond the second substrate to the first substrate. 